ESLint Plugin De Morgan

An ESLint plugin that enforces logical consistency by transforming negated boolean expressions according to De Morgan’s laws.

This plugin automatically rewrites negated conjunctions and disjunctions to improve code clarity and reduce potential logical errors.

Why

In Boolean algebra, De Morgan’s laws are two transformation rules that are both valid rules of inference. They are named after Augustus De Morgan and are fundamental in the fields of mathematics, computer science, and digital logic. The laws state that:

First Law:

¬(A ∧ B) ≡ (¬A) ∨ (¬B)

Second Law:

¬(A ∨ B) ≡ (¬A) ∧ (¬B)

Using these principles, the plugin provides two ESLint rules:

no-negated-conjunction — Transforms negated conjunctions (i.e. expressions of the form !(A && B)) into the equivalent disjunction of negations (!A || !B).
no-negated-disjunction — Transforms negated disjunctions (i.e. expressions of the form !(A || B)) into the equivalent conjunction of negations (!A && !B).

These transformations are grounded in Boolean algebra and can help make the logic of your code more explicit and easier to understand.

Why Use De Morgan’s Laws?

De Morgan’s laws are a cornerstone of Boolean algebra and have several practical benefits in programming:

Clarity: Rewriting complex negations often results in expressions that more clearly communicate the underlying logic.
Avoiding Logical Errors: When dealing with nested logical expressions, small mistakes in the placement of negations can lead to subtle bugs. By enforcing a consistent style based on well-known laws, the plugin helps reduce such errors.
Simplification: In some cases, the transformed expression may be simpler to evaluate and optimize, both for human readers and for compilers / interpreters.

Examples

Base example

Before:

if (!(a && b)) {
  /* ... */
}

After:

if (!a || !b) {
  /* ... */
}

More complex example

Before:

if (!(a || !b || c >= 10 || d !== e)) {
  /* ... */
}

After:

if (!a && b && c < 10 && d === e) {
  /* ... */
}

Installation

You'll first need to install ESLint:

npm install --save-dev eslint

Next, install eslint-plugin-de-morgan:

npm install --save-dev eslint-plugin-de-morgan

Usage

The easiest way to use eslint-plugin-de-morgan is to use ready-made config.

Flat Config (`eslint.config.js`)

import deMorgan from 'eslint-plugin-de-morgan'

export default [
  deMorgan.configs.recommended,
]

Legacy Config (`.eslintrc.js`)

module.exports = {
  extends: [
    'plugin:de-morgan/recommended-legacy',
  ],
}

Rules

🔧 Automatically fixable by the --fix CLI option.

Name	Description	🔧
no-negated-conjunction	Transforms the negation of a conjunction into the equivalent disjunction	🔧
no-negated-disjunction	Transforms the negation of a disjunction into the equivalent conjunction	🔧

Further Reading

Versioning Policy

This plugin is following Semantic Versioning and ESLint's Semantic Versioning Policy.

Contributing

See Contributing Guide.

License

MIT © Azat S.